Micro Spectroscopic Photoacoustic (μsPA) imaging of advanced carotid atherosclerosis

Highlights • We built a micro-spectroscopic photoacoustic imaging setup, allowing spectral imaging throughout the section. • Spectral differences were primarily due to differences in hydrocarbon chain length and number of unsaturated bonds. • PA signal intensity was most strongly correlated with sphingomyelin and cholesteryl ester area in MALDI-MSI. • The spectral feature of lipids abundant in necrotic core can be used for detection of atherosclerosis with features of instability.
Atherosclerosis is a lipid-driven and an inflammatory disease of the artery walls. The composition of atherosclerotic plaque stratifies the risk of a specific plaque to cause a cardiovascular event. In an optical resolution photoacoustic microscopy setup, of 45 μm resolution, we extracted plaque lipid photoacoustic (PA) spectral signatures of human endarterectomy samples in the range of 1150–1240 nm, using matrix assisted laser desorption ionization mass spectrometry imaging as a reference. We found plaque PA signals to correlate best with sphingomyelins and cholesteryl esters. PA signal spectral variations within the plaque area were compared to reference molecular patterns and absorption spectra of lipid laboratory standards. Variability in the lipid spectroscopic features extracted by principal component analysis of all samples revealed three distinct components with peaks at: 1164, 1188, 1196 and 1210 nm. This result will guide the development of PA-based atherosclerosis disease staging capitalizing on lipidomics of atherosclerotic tissue.